My mechanic just diagnosed my bonneville with a bad ecm. He is telling me that I have to go to the GM dealer to get it replaced because of programming issues for the new ecm. Can someone tell me if this is really necessary? All the research that I've done never mentions this. I believe that I got an accurate diagnosis but like everyone I am short on cash. What is the correct process to do this and which brands are best? All the Internet sites that sell these ask for Vin numbers so they can program and claim that they are ready to "plug and play". What'* the real story??? Thanks in advance for anyones help!

I got one for my 96' PA from PCM for Less a few years back, just gave them the VIN and they programmed it and when I got it I just plugged it in and was good to go.
I think I paid like 125.00 plus shipping for my ore-programmed ECM, yours may be a bit more, not sure though.

Your mechanic is correct. In order to install a new PCM, the dealer must program your new PCM with the correct information due to the fact that new PCM'* come "unprogrammed". This can only be done with a Tech2 programmer that only GM dealers have.

And you cannot simply run to the junkyard and get one from an identical car either. All modules in your car communicate via the CAN network bus and they all share the same vin. If you have a vin mismatch, your radio won't work.

Is the 03' PCM that much different than the 96' ones?
I thought anybody with the ability to flash a VIN to a PCM/ECM could do it?
Some of these places will sell you a new or used PCM, and I know that can flash some PCM'*, just not sure which ones they cannot do..

The newer PCM'* communicate with many other modules in the vehicle. If there is a data/vin mismatch, things wont work correctly. If you swap a vin specific stereo from one car to another, it won't work period. Unless you reprogram the vin in the radio. And yes, there is a huge difference from the 96 pcms and the 2000+ pcms.

Ok so now I have an appointment with the local gm dealership. They are willing to match ac/Delco eBay price for pcm. I know that they will flash correctly and they will confirm the diagnosis. Really tired of an unreliable vehicle

Can the VIN be reprogrammed on a second hand PCM?

I thought it could, but Mike said it could not.
I know a guy in Ohio that Dyno'* cars and programs PCM'* for a living, he also will program PCM'* and ship them to customers in cases like this, I know he did 1996 and pre 1996 PCM'* all the time, I also know he did newer cars.
One of the guys I met a while back on another forum was working on flashing newer caddy PCM'*..
Since the OP is getting a decent deal then he may as well go for it, it will save time for sure.

Aren't you the guy who said in another post(6/28/16) that you had a P0420 code? I hope your mechanic knows what he'* doing instead of just throwing parts at it. GOOD LUCK!

Hopefully he knows what he is doing, there are only a few single issues that I have heard of causing an ECM/PCM to need to be replaced, like the fuel injector circuit.
A good bit of the time if an ECM/PCM is going bad there are several issues, at least from what I have heard.